The present invention relates to a toner for electrophotography, in particular, which is composed of domain resin containing a coloring agent and being dispersed in a matrix resin, and a method for producing the same.
As a toner for electrophotography, there have been generally used the ones which are prepared by the steps of melting and kneading a matrix resin as a binder, a coloring agent and the like, pulverizing the kneaded material, and classifying the pulverized material to have a uniform specified particle size distribution.
Coloring agents are, however, irregularly exposed on the surface of such a toner obtained by the method of pulverizing as noted above. Since the coloring agent is inferior in moisture resistance and environmental resistance, there arise some problems in uniformity in electrification amount on each toner particle and so does in stability against storage and environment. Moreover, the coloring agent may be separated from toner surface to adhere to carrier surface, causing instability of electrification ability.
To prevent adverse effects caused by exposure of the coloring agent onto the toner surface, a micro-dispersion technique has been proposed in which the coloring agent is put into a specified phase in the toner (for example, Japanese Patent Laid-Open Publication SHO 62-17753). While the coloring agent may be suppressed from being exposed until the kneading step in the micro-dispersion technique, the problem of exposure of the coloring agent on the surface remains unsolved after pulverizing.
Further, in the method for producing a toner by pulverizing a kneaded material, a toner is liable to be over-pulverized. The resulting particle size distribution is considerably large in width. The classification yield of the toner having a specific particle size range is quite low. In particular for enhancing the image quality of electrophotographical copy images, there have been demanded a toner having a small particle size and a narrow particle size distribution, whereas conventional toners are more likely to result in an over-pulverization and moreover in a markedly low yield after classification, disadvantageously.
As a method for producing a toner having a uniform particle size distribution efficiently with the coloring agent kept from being exposed on the surface, it is possible to apply a suspension polymerization method in which the toner particles are formed in a solution, or a spray-dry method. However, the resulting particles in these methods are so high in the degree of sphericality as to result in a problem of residual toner in a conventional general-purpose cleaning method, or the blade-cleaning method. To avoid this problem, it is necessary to adopt a complex cleaning method. Moreover, since the method for producing a toner by the suspension polymerization method or the like is a new method, there is another problem that conventional facilities for the kneading and pulverizing method can not be used, necessitating additional investment.